The present invention relates to a pivoting door thrust reverser for a turbojet engine, more particularly a thust reverser having panels mounted on the engine cowling and cooperating with the pivoting thrust reverser door.
Turbofan-type turbojet engines are well known in the art and typically comprise a fan at the front of the turbojet engine which directs a flow of bypass air through a duct bounded on the inside by the engine cowling and on the outside by a fan cowling. The generally annular duct bounded by the engine cowling and the fan cowling may channel both the bypass flow and the primary exhaust gas flow at a downstream portion or may channel only the bypass flow.
In aircraft on which the turbojet engine is mounted outside of the airframe structure, the fan cowling and the engine cowling are configured to form boundaries of the bypass flow duct and to provide aerodynamic outer surfaces to reduce drag.
FIGS. 1 and 2 illustrate a known pivoting door-type thrust reverser associated with the fan cowling of a turbofan-type turbojet engine. As illustrated in FIG. 1, the upstream portion of the fan cowling which defines the outer limits of the bypass flow duct and which is generally concentrically arranged about the turbojet engine (not shown) is designated as 1 and generally comprises an external cowling panel and an internal cowling panel interconnected by a frame 6. The outer surface of the external cowling panel has an aerodynamic surface over which the air external to the engine passes during aircraft flight in the direction of arrow 12. The inner surface of the inner cowling panel defines the outer boundary of the bypass flow duct through which the bypass air flow passes in the direction of arrow 14.
The fan cowling also comprises a trust reverser, illustrated generally at 2, and a downstream fairing 3. The thrust reverser 2 comprises a door 7 pivotally attached to the cowling such that it is movable between a closed, forward thrust position, illustrated in FIG. 1, and an open, reverse thrust position in which the upstream end (towards the left as viewed in FIG. 1) of the thrust reverser door 7 is moved outwardly from the cowling, while a downstream portion is moved inwardly into the bypass flow duct airstream so as to redirect at least a portion of the bypass flow through an opening in the fan cowling in a direction that has a reverse thrust component.
An actuator 8 for moving the door 7 between its forward thrust and reverse thrust positions may comprise a hydraulic cylinder mounted to the frame 6, and having an extendible and retractable piston rod connected to the thrust reverser door 7.
The thrust reverser door 7 has an outer door panel 9 and an inner door panel 11 joined together by an internal structure. The upstream end of the door 7 may have a deflector 13 to maximize the efficiency of the thrust reverser when the door 7 is in the reverse thrust position. When the door is in the forward thrust position, as illustrated in FIG. 1, the outer door panel 9 is substantially flush with the external surfaces of the upstream panel and the downstream fairing 3.
As illustrated in FIG. 2, a plurality of thrust reverser doors 7 may be incorporated into the fan cowling, such doors being circumferentially spaced around the periphery of the fan cowling. A portion 18 of the fan cowling extends from an upstream portion 4 of the cowling axially between adjacent thrust reverser doors 7 to provide structural rigidity to the fan cowling and to provide pivot mounting points for attaching the doors 7 to the fan cowling. French Patents 1,482,538 and 2,030,034 illustrate typical, known thrust reversers.
U.S. Pat. No. 3,605,411 discloses a pivoting door-type thrust reverser in which the deflector mounted on the upstream or forward end of the thrust reverser door is movable to an extended position when the door is in the reverse thrust position.
French Patent 2,618,853 discloses a thrust reverser in which the deflector is retracted when the door is in its forward thrust position to optimize engine performance.
In some applications, as illustrated in FIG. 1, the deflector 13 projects from the inner panel 11 of the thrust reverser door 7 even when the door is in its forward thrust position without extending into the bypass flow duct. This forms a cavity 16 facing inwardly into the bypass flow duct which will slightly degrade engine performance.
French Patent 2,680,547 discloses a thrust reverser having a combination of spoilers and deflectors to attempt to optimize the direction of exhaust flow.
The above-described known thrust reversers incur major drawbacks because of the aerodynamic size constraints on the flow passage cleared by the forward portion of the thrust reverser door which cause the door to be biased in the open, thrust reversing direction. The full cross-section of the flow passage must be larger than the associated duct cross-section in a plane taken upstream, or forward, of the door on account of the pressure losses due to the gas flow deflection since the downstream, or rearward portion of the duct unobstructed by the inwardly protruding portion of the thrust reverser door is minimized in order to produce an appropriate reverse thrust force.
Quite obviously, the bias of the doors toward the open or reverse thrust position is a safety drawback. The reverser would be safer if the thrust reverser door was biased towards the closed or forward thrust position. This consideration also applies to a thrust reverser door that would tend to close again under pressure even if it was partially deployed towards the thrust reversing position.
In some cases, the effect of the pressure acting on the thrust reverser door is such that very high stresses are transmitted through the thrust reverser door actuators between their attachment points to the upstream portion of the cowling and the doors. As a consequence, this structure and the door locking mechanisms must be undesirably heavy.
European Patent Application 0 413 635 discloses a thrust reverser with doors associated with an upstream panel having stationary pivots about which the panels move. The panel is moved by the associated thrust reverser door using connecting rods, in the same direction of rotation as the door. In this design, the panel acts as a shield against the flow of the reverse thrust gases contacting the thrust reverser door when the door and the panel are in their reverse thrust positions, making it impossible to achieve optimal guidance of the reverse flow gases.